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Preamplifier design : Input and Load reflection coefficient

S

sthim

Jan 1, 1970
0
The preamplifier that I can trying to design is suppose to have a
constant vswr that is suppose to be within certain nf limits. If I
manage to figure out a load reflection coefficient value that would
make the vswr fall with the required nf circle, that I will be able to
design the matching networks. However, I am unable to do that. At
that moment, I have managed to find the vswr circle using the input
reflcetion coefficient relation. I would need to find the load
reflection coefficient using this parameter and I am not sure how to
do that. Or I may be approaching this problem in an incorrect way.

sthim2003
 
R

Rene Tschaggelar

Jan 1, 1970
0
sthim said:
The preamplifier that I can trying to design is suppose to have a
constant vswr that is suppose to be within certain nf limits. If I
manage to figure out a load reflection coefficient value that would
make the vswr fall with the required nf circle, that I will be able to
design the matching networks. However, I am unable to do that. At
that moment, I have managed to find the vswr circle using the input
reflcetion coefficient relation. I would need to find the load
reflection coefficient using this parameter and I am not sure how to
do that. Or I may be approaching this problem in an incorrect way.

Are you simulating the design or are you building it.
In case of the later you need to measure the stuff.

Input and output reflections are independent of each other,
at least from a certain complexity up. That is the point of an
amplifier, to decouple input from output.

Rene
 
A

Active8

Jan 1, 1970
0
On 18 Jan 2004 17:20:46 -0800, [email protected] said...
The preamplifier that I can trying to design is suppose to have a
constant vswr that is suppose to be within certain nf limits. If I
manage to figure out a load reflection coefficient value that would
make the vswr fall with the required nf circle, that I will be able to
design the matching networks. However, I am unable to do that. At
that moment, I have managed to find the vswr circle using the input
reflcetion coefficient relation. I would need to find the load
reflection coefficient using this parameter and I am not sure how to
do that. Or I may be approaching this problem in an incorrect way.

sthim2003
Try searching google for an app note from Motorola or HP on Small
Signal Amplifier Design Linvill Method or some combination of those
words.

What transistor is it? Doesn't the spec sheet give a bias point and
input reflection coefficient (not a vswr circle) for optimum NF?
 
P

Precious Pup

Jan 1, 1970
0
Input and output reflections are independent of each other,...


S12 is never 0. Design equations for simultaneous I/0 match are available.
 
R

Rene Tschaggelar

Jan 1, 1970
0
Precious said:
S12 is never 0. Design equations for simultaneous I/0 match are available.

Splitting hairs ?
I said it was dependent on the complexity. A standard OpAmp
with sufficient gain, sufficient feedback has no coupling between
the two. It ideally has infinite input impedance, zero output
impedance and with some external parts can be made to match whatever
on both sides independently.

Sure, a single transistor looks a bit different.


Rene
 
S

sthim

Jan 1, 1970
0
I am only simulating it at the moment. I am going to use a Agilent
ATF series PHEMT.

sthim2003
 
P

Precious Pup

Jan 1, 1970
0
Rene said:
Splitting hairs ?

Not really.
I said it was dependent on the complexity. A standard OpAmp
with sufficient gain, sufficient feedback has no coupling between
the two. It ideally has infinite input impedance, zero output
impedance and with some external parts can be made to match whatever
on both sides independently.

He is likely talking about an RF/microwave preamp. He didn't mention an op-amp.
Sure, a single transistor looks a bit different.

yeah, a "bit."
 
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